CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury	Noncontrolling Interests	Opening retained earnings adjustment: adoption of new accounting standard	Opening retained earnings adjustment: adoption of new accounting standard Retained Earnings	Adjusted balance, April 1	Adjusted balance, April 1 Common Stock	Adjusted balance, April 1 Additional Paid-in Capital	Adjusted balance, April 1 Retained Earnings	Adjusted balance, April 1 Accumulated Other Comprehensive Loss	Adjusted balance, April 1 Treasury	Adjusted balance, April 1 Noncontrolling Interests
Beginning balance (shares) at Mar. 31, 2020		272,000,000									272,000,000
Beginning balance (shares) at Mar. 31, 2020						(110,000,000)									(110,000,000)
Beginning balance at Mar. 31, 2020	$ 5,309	$ 2	$ 6,663	$ 13,022	$ (1,703)	$ (12,892)	$ 217	$ (13)	$ (13)	$ 5,296	$ 2	$ 6,663	$ 13,009	$ (1,703)	$ (12,892)	$ 217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans	(3)		21			$ (24)
Share-based compensation	23		23
Payments to noncontrolling interests	(43)						(43)
Other comprehensive income (loss)	(32)				(32)
Net income	$ 483			444			39
Repurchase of common stock (shares)	0
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	$ 3		3
Cash dividends declared	(67)			(67)
Other	(7)		1	(2)			(6)
Ending balance (shares) at Jun. 30, 2020		272,000,000
Ending balance (shares) at Jun. 30, 2020						(110,000,000)
Ending balance at Jun. 30, 2020	$ 5,653	$ 2	6,711	13,384	(1,735)	$ (12,916)	207
Beginning balance (shares) at Mar. 31, 2021		273,000,000
Beginning balance (shares) at Mar. 31, 2021	(115,000,000)					(115,000,000)
Beginning balance at Mar. 31, 2021	$ 175	$ 2	6,925	8,202	(1,480)	$ (13,670)	196
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans (shares)		1,000,000
Issuance of shares under employee plans	12		71			$ (59)
Share-based compensation	33		33
Payments to noncontrolling interests	(39)						(39)
Other comprehensive income (loss)	23				23
Net income	525			486			39
Repurchase of common stock (shares)						(4,000,000)
Repurchase of common stock	(1,000)		(150)			$ (850)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	8		178		(170)
Reclassification of McKesson Europe redeemable noncontrolling interests	287						287
Cash dividends declared	(65)			(65)
Other	$ (4)			(5)			1
Ending balance (shares) at Jun. 30, 2021		274,000,000
Ending balance (shares) at Jun. 30, 2021	(119,000,000)					(119,000,000)
Ending balance at Jun. 30, 2021	$ (45)	$ 2	$ 7,057	$ 8,618	$ (1,627)	$ (14,579)	$ 484